Integrated power stages, used in voltage regulators, have various monitoring and protection features. When a protection event (fault) occurs in a power stage, the power stage should be identified/flagged to the controller which reacts accordingly to ensure safe operation of the entire voltage regulator system. A reported fault indicates a critical condition with high stress levels on the power stage and/or load that require immediate action to prevent imminent catastrophic failure. For example, after fault detection, the controller can set the output of the faulty power stage to tri-state and so that the output voltage is discharged by the load. In another approach, the controller permanently turns on the low-side power transistor of the faulty power stage to prevent destruction of the load. In yet another approach, the controller continues operation until a more severe condition is detected.
Typical protection features implemented in an integrated power stage include: Over Temperature Protection (OTP); Over Current Protection (OCP); High Side Short/Control power transistor Short Detection (HSS); and BOOT voltage under voltage lockout (BOOT UVLO). The BOOT UVLO fault condition indicates that the high-side power transistor of a power stage is being driven with an insufficiently low voltage. Fault conditions are typically reported from an individual power stage to the controller by requiring each power stage to signal a fault condition at a dedicated pin (widely referred to as TMON or TMON/FAULT). This pin is often used to report power stage temperature information when no faults are detected. In the event of a fault, the fault is reported over the dedicated pin using out-of-band signalling i.e. by using signal levels outside of the nominal range used to report temperature information over the pin. In a simplified design, the dedicated pin (TMON or TMON/FAULT) from all power stages are connected to the same signal line (e.g. by a wired-OR connection), and this common connection is coupled to a corresponding dedicated pin of the controller. This simplified implementation is widely adopted in multiphase voltage regulator system, were each power stage provides one phase (current) of the system. With this simplification, the controller cannot distinguish among faults reported by different power stages. As such, the controller cannot identify which power stage is communicating a fault. As a consequence, the controller typically either ignores the fault or shuts down the entire system.